1. Field of the Invention
Embodiments of the invention generally relate to implantable cardiac devices, including monitoring devices, pacemakers, defibrillators and cardioverters, which monitor, detect and classify cardiac events, for example atrial tachyarrhythmias. More particularly, embodiments of the invention relate to a method and device for detecting Atrial Fibrillation or Atrial Flutter by evaluating ventricular signals. Further, embodiments of the invention relate to methods for monitoring atrial events for use in implantable devices without atrial electrodes.
2. Description of the Related Art
There are previously proposed methods for detecting atrial tachyarrhythmias and a determination of their being stable or unstable. However, an otherwise simple task is complicated by the fact that a multi-chamber pacemaker or ICD may not “see” all of the atrial complexes due to some of these falling in cross-chamber blanking periods, such as post-ventricular-pace blanking and far-field blanking periods.
It is known from the prior art to use a so called “X-out-of-Y” criterion to detect an ongoing atrial tachyarrhythmia. The U.S. Pat. No. 6,671,548 B1 for example describes use of such a “X-out-of-Y” criterion. This criterion declares detection of an atrial tachyarrhythmia when X number of intervals among most recent Y number of atrial intervals are found to be shorter than an interval limit corresponding to the tachyarrhythmia rate limit. The numbers X, Y and the tachyarrhythmia rate limit may be user defined, e.g., pre-defined or may be programmable. As is clear, the “X-out-of-Y” criterion accommodates for undersensing of some of the atrial events.